The past decade has seen a revolution in computing. The advent and proliferation of personal computers has transformed the computing environment from one of climate-controlled computer rooms with technician acolytes to notebook computers and pen-based personal communicators that users carry wherever they go. A significant expansion of computing applications is a concomitant result of this changing computer environment. In the past, computers provided, primarily, accounting, data reduction, and data-base management applications. They now, additionally, provide a variety of voice-messaging and multimedia applications.
Multimedia applications are, generally, those applications that provide combined video and audio output. They include business presentations, communications packages, and entertainment applications. These applications, particularly the entertainment applications (e.g., games, music, videos etc.), require reasonably high quality audio output. Whether it is the roar of a Tyrannosaurus Rex emanating from a Jurassic Park.TM. CD-ROM-game or the subtle intonations of one's favorite Verdi aria reproduced for a multi-media CD-ROM encyclopedia tour of "La Scala", sound reproduction plays a crucial role in the effectiveness of a multi-media presentation. But, even if one provides otherwise perfect sound reproduction, there are "sound effects", created by the listening environment, which impart a distinctive character to the sound a listener hears and these effects, or the absence of them, may have a subtle, but profound, effect on a listener's perception of the reproduced sound.
One of the commonly recognized sound effects is that of reverberation. Reverberation is the result of sound traveling different paths to reach a listener's ear. Sound travelling along a direct path will reach the ear first, that which is reflected once before it reaches the ear may reach it next, that which is reflected twice may reach it next, etc. The reverberation characteristics of a dinosaur-filled jungle would differ considerably from those of a concert hall and, to improve users' listening experiences, it is highly desirable to provide a reverberation capability for multimedia systems. Reverberation, if subject to the control of a listener, could be tailored, at the listener's command, to emulate the "full" sound of a concert hall, or the "dead" sound of a field of new-fallen snow.
Although listener-controlled reverberation effects are commercially available on some high-fidelity sound systems and professional audio signal processing devices, these systems generally employ either specialized hardware such as delay lines, multipliers, and adders or digital signal processor chips (DSPs) to produce and combine the multiply-delayed versions of an audio signal necessary to achieve the reverberation effect. Although one could use either of these approaches to produce reverberation effects for a multi-media system, multi-media applications, especially personal-computer-based multi-media applications for home use, are highly cost-sensitive. The additional expense of specialized hardware, whether it is based on DSPs or discrete delay lines and adders, may be prohibitive for an inexpensive personal-computer based system. Additionally, personal computer expansion slots are frequently in short supply and an additional expansion slot may not be available for sound-processing hardware. For these reasons it would be highly desirable to provide reverberation sound effects for personal-computer-based multi-media systems without the requirement for additional equipment.